Currently I run about 7 km every day. I feel that this is too much for me, as I also do some fitness every other day. It is just too time consuming with my new job. I just want to stay in shape and I have no intentions on running marathons etc.
My question is: Considering my muscles and cartilages on the long run (20-30 years). What is better for my body?
Honestly, if just general fitness is your goal, then around 5k every other day is perfectly fine for your needs. You really only need to run more if you have specific goals and are training for running races.
While 7-8k is not overly long, I wouldn't really run that every other day. I'd cycle it a bit, so that you have a couple of 5k runs then a slightly longer run, 7-10k. You'd be perfectly fine to have a day or two off between runs, especially if you are doing other supplemental fitness.
